Process for preparing an alkenylphosphonic acid derivative by reacting a phosphonic acid derivative with an alkyne in the presence of a catalyst complex system, wherein the catalyst complex system comprises (a) nickel and (b) a phosphine having at least two trivalent phosphorus atoms and/or (c) a phosphine having one trivalent phosphorus atom and the alkyne is added only after the phosphonic acid derivative has been brought into contact with the catalyst complex system for at least one minute.